The present invention is directed to the field of disinfecting wastewater.
The pollution problem posed by the disposal of wastewater from domestic and industrial sewage is a serious problem, especially in densely populated areas. In such areas, literally millions of gallons of untreated or inadequately treated wastewater from domestic and industrial sewage are discharged into streams, lakes, and the like. The discharge of such inadequately treated wastewater can cause severe health problems as well as being esthetically most undesirable. A variety of infectious microorganisms are found in municipal wastewaters, which, if the water is not disinfected, can lead to outbreaks of gastroenteritis, salmonellosis, shigellosis, typhoid, ear infections from Pseudomonas aeruginosa, and infectious hepatitis.
Chlorine has been traditionally employed for disinfecting water and wastewater. However, recent reports concerning the carcinogenic effects of chlorinated compounds resulting from chlorine disinfection have stimulated the search for less potentially harmful disinfectants. It has been found that the indiscriminate chlorination of wastewaters results in the formation of halogenated compounds which are toxic to aquatic life and potentially toxic to humans. Further, chlorination can satisfy prospective Federal water discharge standards only with such high dosages that expensive dechlorination is required as a further process step.
Researchers have investigated the use of ozone, chlorine dioxide, ultra-violet light, iodine, bromine, and bromine chloride as possible alternatives to chlorine disinfection of wastewater. Although all of these alternatives are effective in disinfecting water and wastewater to various degrees, in general, these alternatives are more costly than the use of chlorine. Thus, there is an urgent need to develop an effective, low cost, alternative disinfectant which meets current and future Federal, state, and local water pollution standards.
SO.sub.2 has long been known to the food processing and wine industries for disinfection of equipment and beverages. For example, U.S. Pat. No. 623,105 issued Apr. 11, 1899 describes purifying sugar syrup by passing SO.sub.2 into the syrup. Further, the use of SO.sub.2 for purification of wastewater is described in U.S. Pat. Nos. 2,171,203, 3,522,173, 3,948,774, and 4,123,355. In the process, sufficient SO.sub.2 is used to reduce the PH of the wastewater, generally in the order of 2 to 3.
The use of SO.sub.2 for disinfecting wastewater is an economically attractive alternative to the use of chlorine for disinfecting wastewater, without the problem of generation of chlorinated carcinogenic compounds. However, none of the processes described in the aforementioned patents has achieved any significant acceptance. The processes have not demonstrated on any large scale the ability to meet the 1983 U.S. Environmental Protection Agency's standards for water discharge for irrigation, recreation, and industrial use. This is most likely the result of a lack of a fundamental understanding of how a process utilizing SO.sub.2 for disinfecting wastewater is to be controlled and operated for efficient and effective disinfection. Further, large quantities of SO.sub.2 are required.
Therefore, it is clear that there is an urgent need for an effective, low cost, and efficient process for disinfecting wastewater utilizing SO.sub.2.